1. Field of the Invention
The present invention relates to a solid-state image sensing apparatus for use in an input portion of an information processing apparatus such as a facsimile machine, a video camera, a copying machine and the like. More particularly, the present invention relates to a solid-state image sensing apparatus formed by stacking a photosensitive layer on a single crystal semiconductor circuit substrate having a signal charge storage portion, a signal reading circuit, a scanning circuit, a drive circuit and the like, and a method of manufacturing the same.
2. Related Background Art
Recently, solid-image sensing apparatuses utilizing semiconductors have been widely used and there arises a desire of solid-state image sensing device which has further improved performance and the cost of which can be further reduced.
Hitherto, the main portion of solid-state image sensing devices has been mainly constituted, similarly to CCDs and MOS solid-state image sensing apparatuses for example, in such a manner that a light receiving device portion, a signal charge storage portion, a signal reading circuit, a scanning circuit, a signal processing circuit, and the like are formed on the same semiconductor substrate. Furthermore, laminated solid-state image sensing apparatuses, in which a photo-conductive film serving as a light receiving device is stacked on a semiconductor substrate, have been disclosed.
In order to describe the conventional technology, an example of an MOS solid-state image sensing apparatus will now be described with reference to FIG. 1.
Referring to FIG. 1, reference numeral 101 represents a p.sup.- type silicon substrate, 102 represents a p.sup.+ region, 103 represents a p.sup.- region, 104 represents a n.sup.+ source region, 105 represent a n.sup.- type drain region, 106 represents a gate oxidized film, 107 represents a poly-silicon for a gate electrode, 108 represents a first silicon oxidized film, 109 represents an electrode, and 116 represents a passivation film.
In this case, a light receiving device comprises an n.sup.+ p.sup.- p.sup.+ diode composed of the n.sup.+ source region 104, the p.sup.- region 103 and p.sup.+ region 102, and this diode also serves as a signal charge storage portion.
FIG. 2 shows a conventional example of a stacked type solid-state image sensing apparatus in which a photosensitive film is stacked on the aforesaid solid-state image sensing apparatus. Referring to FIG. 2, reference numeral 110 represents a first pixel electrode, 111 represents a second silicon oxidized film, 112 represent a third silicon oxidized film, 113 represents a second pixel electrode, 114 represents a photo-conductive film serving as a photosensitive film, and 115 represents a transparent electrode, and residual elements are the same as those shown in FIG. 3.
However, the aforesaid conventional technologies encountered the following problems to be solved.
In the conventional solid-state image sensing apparatus shown in FIG. 1, the thickness and the density of impurities of the p.sup.- region of the n.sup.+ p.sup.- p.sup.+ diode serving as the light receiving device have been determined in order to obtain desired light absorbing characteristics. However, it is impossible for the n.sup.+ p.sup.- p.sup.+ diode, the thickness and the density of the impurities of which have been determined to obtain desired light receiving characteristics, to obtain a desired storage capacity because the n.sup.+ p.sup.- p.sup.+ diode also serves as a signal charge storage capacity. Therefore, there arises a problem in that the charge quantity of a saturation signal is reduced and dynamic range is undesirably lowered. If the p.sup.+ region is designed to have a desired storage capacity, desired light receiving characteristics cannot be obtained.
That is, the aforesaid structure encounters a problem that both desired characteristics for the light receiving device and the storage capacity characteristics cannot easily be obtained. This problem experienced with the conventional case in which the light receiving device comprises the n.sup.+ p.sup.- p.sup.+ diode also arises in the other structure.
In the conventional laminated solid-state image sensing apparatus shown in FIG. 2, the photo-conductive film 114 serves as a light receiving device and the storage capacity can be mainly determined by the junction capacity of the n.sup.+ source region 104. Therefore, the problem described with reference to FIG. 1 can be overcome, but the following problem arises.
Since the semiconductor circuit substrate shown in FIG. 2 and having a variety of devices and circuits formed thereon has excessively large projections and pits in its surface on which the photo-conductive film will be formed, problems arise in that dark currents increase in the photo-conductive film and the resolution deteriorates if the photo-conductive film is stacked in this state. Therefore, there is a necessity of flattening the surface on which the photo-conductive film will be formed. Accordingly, the inventors of the present invention employed the following manufacturing process and manufactured the apparatus shown in FIG. 2. The process will now be briefly described with reference to FIGS. 3 to 9.
(1) After devices have been formed on a semiconductor substrate by using a MOS process, the second silicon oxidized film 111 serving as an interlayer insulating film is deposited and a contact hole is formed on a source region (see FIG. 3).
(2) The first pixel electrode 110 is formed (see FIG. 4).
(3) The third silicon oxidized film 112 is deposited and a resist is applied, so that a flat surface is formed (see FIG. 5).
(4) The entire surface is etched while making the same the etching rate for the resist and that for the third silicon oxidized film 112, for example, using a parallel-flat plate type dry etching apparatus. Thus, the flat third silicon oxidized film 112 can be obtained (see FIG. 6).
(5) A contact hole for establishing a contact between the first pixel electrode 110 and the second pixel electrode 113 is formed (see FIG. 7).
(6) The second pixel electrode 113 is formed (see FIG. 8).
(7) The photo-conductive film 114 is stacked (see FIG. 9).
That is, the aforesaid process requires four photomasks after the semiconductor circuit has been formed in each of process (1) for forming the contact hole, (2) for forming the first pixel electrode, (5) for forming the contact hole and (6) for forming the second pixel electrode.
Therefore, the aforesaid conventional laminated-type solid-state image sensing apparatus encounters problems of a complicated manufacturing process, a short circuit between electrodes, and unsatisfactory yield caused from them.
Although the aforesaid descriptions were made about the MOS solid-state image sensing apparatus and the laminated type solid-state image sensing apparatus as the conventional example, any of the solid-state image sensing apparatus encounters the aforesaid problem because the CCD type, SIT type and the bipolar type solid-state image sensing apparatuses have the light receiving portion and the signal charge storage portion which structured basically similarly to the aforesaid apparatuses.